Ternary mixtures of biodegradable polyesters and products manufactured from them

ABSTRACT

The invention relates to a mixture of biodegradable polyesters which includes an aromatic-aliphatic polyester (A), an aliphatic polyester (B) and a polylactic acid polymer (C) in which the concentration of A varies, with respect to (A+B) in the range between 40 and 70% by weight, and the concentration of C with respect of (A+B+C) is of between 6 and 30% by weight.

The present invention relates to mixtures of biodegradable polyesterswhich include at least three polyesters in proportions whereby it ispossible to provide biodegradable film with improved characteristicscompared to the individual initial polyesters and demonstrating, inparticular, properties of considerable strength, both longitudinally ofand transverse the direction of the formation of the film, transparencyand rigidity.

Film manufactured from such mixtures will prove particularly useful infood packaging, for mulching, for silage and in various otherapplications.

THE PRIOR ART

Conventional polymers such as low or high-density polyethylene arecharacterised not only by excellent flexibility and water resistance,but also by a good level of transparency and by excellent resistance totearing. These polymers are used, for example, for sacks and bags, aspackaging material and as film for agricultural mulching. However, theirpoor biodegradability has caused a problem of visual pollution which hassteadily worsened over the past few decades.

Polymers such as L-polylactic, D,L-polylactic or D-polylactic acid andcopolymers thereof are thermoplastic materials which are biodegradable,come from a renewable source, are transparent and have excellentresistance to mould and are thus well suited to packaging food products,contributing to preserving the organoleptic qualities thereof. Thesematerials, however, break down only slowly in the soil and, ifcomposted, decompose only at high temperatures. However their maindrawback is that the thin film obtained under normal conditions, byeither the blown or cast methods, has a low tear resistance. Inaddition, these films are very stiff and thus unsuitable for mulching,for making food packaging bags, bin liners or other packaging filmswhich do, however, require considerable strength.

The aliphatic polyesters, on the other hand, which are mainlyconstituted by monomers from renewable sources, based on diacids anddiols, such as polymers of sebacic, brassylic or azelaic acid, forexample, have the huge disadvantage of being highly anisotropic, withregard to resistance to both longitudinal and transverse tearing, andalso show extremely poor resistance to longitudinal tearing. Thesecharacteristics also make film produced from these resins unsuitable foruse in mulching, in food packaging or for bin liners and the like.

Polyhydroxy-acids, such as poly-ε-caprolactone, also have a typicaltendency to a transverse orientation.

In order to maintain biodegradable characteristics conforming with theCEN 13432 method, biodegradable aliphatic-aromatic polymers, inparticular polymers with the aromatic portion constituted byterephthalic acid and the aliphatic portion constituted by diacid diols,and/or hydroxy acids, with a C2–C20 aliphatic chain, either branched ornot (possibly chain extended with isocyanates, anhydrides or epoxides)and, in particular, polymers based on terephthalic acid, adipic acid andbutandiol, must contain quantities of terephthalic acid (as moles of thetotal acid) not exceeding 55% and preferably not exceeding 50%. Examplesof this type of material include Ecoflex by BASF or Eastarbio byEastman, which are strong but with extremely low moduli, of the order of100 MPa or less.

Binary compounds of polylactic acid and aliphatic polyesters have formedthe object of numerous patents. In particular, the Patent EP-0 980894 A1(Mitsui Chemical) describes a significant improvement in tear resistanceand in the balance of mechanical properties in film manufactured frommixtures of polylactic acid and polybutylenesuccinate, with the additionof a plasticizer.

However the films described are not transparent and have fairly lowstrengths, of the order of 120 g according to the JIS P8116 method. Inaddition, the presence of a plasticizer limits use of the film incontact with food products and, since it ages rather quickly, for use asan agricultural mulch.

The U.S. Pat. No. 5,883,199 describes binary compounds of polylacticacid and polyesters, with a polylactic acid content of between 10 and90% and with the polyester forming either a continuous or co-continuousphase. The tear resistance of the compounds described here is very poor,however.

OBJECT, CHARACTERISTICS AND ADVANTAGES OF THE INVENTION

Starting from the need to find a biodegradable material which combinedthe two properties of transparency and tear resistance, it was asurprise to find that if the three different types of polyesterdescribed (lactic acid polymers, aliphatic polyester derived fromdiacids/diols and aromatic aliphatic polyester) were combined inspecific ratios, there was a critical compositional range in which itwas possible to achieve resistance to tearing in both directions,comparable to that of conventional plastics materials such aspolyethylene, moduli of elasticity with values found between those oflow and high-density polyethylene. It was found, even more surprisingly,that it was possible for the transparency of the ternary mixture ofpolyesters of the invention to be comparable to that of the individualcomponent materials, even when drawn.

DESCRIPTION OF THE INVENTION

The invention relates to a mixture of biodegradable polyesters whichincludes:

-   (A) an aromatic-aliphatic polyester with a melting point of between    50 and 170° C. and preferably of between 80° and 120° C.;-   (B) an aliphatic polyester with a molecular weight Mw greater than    40,000, and preferably >60,000 and a melting point of between 40°    and 170° C., preferably of between 50° and 145° C., and even more    preferably of between 55° and 130° C.;-   (C) a polylactic acid polymer containing at least 75% of L-lactic or    D-lactic acid or a combination thereof, with a molecular weight Mw    greater than 30,000;    in which the concentration of A varies, with respect to (A+B), in    the range between 40% and 70% by weight, and the concentration of C    with respect to (A+B+C) is of between 5 and 30%, preferably of    between 5 and 20% by weight.

More in particular, in the mixture of the invention:

-   (A), the aromatic-aliphatic polyester, is biodegradable according to    the CEN13432 standard, it has (at T=23° and Relative Humidity=55%) a    modulus which is less than 150 MPa, lengthens to breaking point by    more than 500% for blown film with a thickness of 25–30 μm, tested    within three days from production;-   (B), the aliphatic polyester, preferably a diacid/diol type and/or a    polyhydroxyacid type, has (at T=23° C. and Relative Humidity=55%) a    modulus of elasticity of between 200 and 1500 MPa and lengthens to    breaking point by more than 20%, preferably more than 100%, for    blown film with a thickness of 25–30 μm, tested within three days of    production;-   (C), the polylactic acid polymer, has a modulus of more than 1,500    MPa.

The mixture of biodegradable polyesters of the invention is obtained ina process which is carried out in a two-screw or one-screw extruder at atemperature of between 100 and 200° C., either by a one-step method or amethod involving separate steps of mixing and then film forming orinjection molding and so on.

In the event of film forming being separate from the mixing operation,it is carried out by means of conventional machinery for polyethyleneextrusion (high or low density), at a heat in the range of 100° to 200°C., preferably of 140 to 197 and more preferably of 185 to 195° C., witha blowing ratio normally in the range of 1.5–5 and a drawing ratio ofbetween 3 and 100, preferably 3 and 25 and produces film with athickness of between 5 and 50 μm.

Films of the invention, with a thickness of between 25–30 μm, show atear resistance in both directions, according to the Elmendorf test, ofbetween 10 and 100 N/mm, preferably of between 15 and 90 N/mm and evenmore preferably of between 20 and 80N/mm, with a ratio of transverse tolongitudinal Elmendorf values of between 4.5 and 0.4, and preferably ofbetween 3 and 0.5. Such films have a modulus of between 150 and 1200MPa, preferably of between 250 and 1000 MPa and prove biodegradable bothin soil and when composted. Such films are also characterised bytransparency, understood as transmittance at the entrance port measuredon the HAZEGUARD SYSTEM XL-211 in the range between 85 and 90% whenformed into a film at a head temperature of between 185° and 200° C.

During the mixing step, type (A) polymers are preferred with an MFI(ASTM standard D 1238-89) of between 1 and 10 dg/min, type (B) polymersare preferred with an MFI of between 1 and 10 dg/min and (C) typepolymers are preferred with an MFI of between 2 and 30 dg/min.

The type (A) polymer family comprises polyesters obtained from thereaction of mixtures which contain (a¹) mixtures of from 35 to 95% molesof adipic acid, or derivatives in the form of esters or mixturesthereof, from 5 to 65% moles of terephthalic acid, or ester derivativesand mixtures thereof, and from 0 to 5% moles of a sulphur-containingcompound, the sum of the percentages of the various components to be100% (a²) a compound with two hydroxyl functions selected from a groupconsisting of C2–C6 alkandiols and C5–C10 cycloalkandiols, the molarratio (a¹):(a²) being in the interval between 0.4:1 and 1.5:1, it beingpossible for the polyester to have a molecular weight Mw of between5,000 and 50,000, a viscosity of between 30 and 350 g/mole (measured in50:50 w/w dichlorobenzene/phenol at a concentration of 0.5% of theweight of the polyester at 25° C.) and a melting point of between 50 and170° C., and preferably of between 90 and 120° C. It is also possible toproduce the polymer using a compound with at least three groups able toform ester bonds.

The polymer (B) is preferably constituted by dicarboxylic aliphaticacids and aliphatic diols, and possibly also by hydroxy acids.Preferably the polymer (B) is also constituted by hydroxyacids. Examplesof diacids which can be used are succinic, oxalic, malonic, glutaric,adipic, pimelic, suberic, undecandioic, dodecandioic, sebacic, azelaicor brassylic acids. Particularly preferred are sebacic, azelaic orbrassylic acid, or mixtures thereof.

Specific glycols are ethylene glycol, diethylene glycol, triethyleneglycol, polyethylene glycol, 1,2- and 1,3-propylene glycol, dipropyleneglycol, 1,3-butandiol, 1,4-butandiol, 3-methyl-1,5-pentandiol,1,6-hexandiol, 1,9-nonandiol, 1,11-undecandiol, 1,13-tridecandiol,neopentyl glycol, polytetramethylene glycol, 1,4-cyclohexane-dimethanoland cyclohexane-diol. These compounds can be used individually and incombination.

Typical hydroxy acids include C₂–C₂₂ hydroxy acids such as, for example,glycolic acid, lactic acid, 3-hydroxybutyric, 4-hydroxybutyric,3-hydroxyvaleric, 4-hydroxyvaleric and 6-hydroxycaproic acid and so on,and also cyclic esters of hydroxycarboxylic acids such as glycolide,dimers of glycolic acid, epsilon-caprolactone and 6-hydroxycaproic acid.These compounds can be used individually or in combination.

All the compounds mentioned above are combined so as to form polyesterswith tensile mechanical characteristics of resistance to elongation >25%and preferably >100% with a modulus of between 200 and 1500 MPa forblown film at least 25–30 μm thick, with a melting point of between 40°and 170° C., preferably of between 50° and 145° C. and more preferablyof between 55° and 130° C.

Particularly preferred are polyesters containing more than 50%, andpreferably more than 70%, moles with respect to the total acid contentof azelaic acid, sebacic acid, brassilic acid or mixture thereof. Alsopreferred are polyhydroxyacids obtained by process of synthesis frombacteria or plants or other biological processes such as copolymers ofhydroxybutirrate and C₅–C₂₀ hydroxyacids.

The type B polymers also include polyamide polyesters in which thepolyester portion is as described above and the polyamide portion can becaprolactam, an aliphatic diamine such as hexamethylenediamine or evenan aminoacid. The B type polyesters may also contain a quantity of lessthan 5% moles of aromatic diacids. Polycarbonates also belong to thetype B polymers.

Biodegradable polyesters forming part of the mixture of the inventioncan be polymerized by polycondensation or, as in the case of glycolideand the lactones, by the open-ring method, as known in the literature.They can be synthetized also by microorganisms or plants. The polyesterscan also be branched polymers, with the introduction of polyfunctionalmonomers such as glycerine, epoxidized soya oil, trimethylolpropane andthe like, or of polycarboxylic acids such as butantetracarboxylic acid.In addition, chain extenders such as difunctional, trifunctional ortetrafunctional anhydrides, for example maleic, trimellitic orpyromellitic anhydride, or expoxy, aliphatic or aromatic iso-cyanatesgroup, can be added to A type polyesters.

The material can be regraded with iso-cyanates either in its moltenstate, at the end of the polymerization reaction or during extrusion, orin its solid state, as described in the Patent Application Novamont WO99/28367. The three types, A, B and C, of polymer can also have chainextenders or cross-linking agents added to them during the mixingoperation.

Higher concentrations of A than those of the range reported above forthe mixture of the invention involve modulus characteristics which aretoo low, while lower concentrations of A bring a deterioration inlaceration characteristics.

Higher concentrations of B than those of the range reported above formixtures of the invention make the film more unbalanced and less strong,while lower concentrations mean that the film is insufficiently rigid.

Concentrations of C polymer below 5% have no significant effect on thebalance of tearing properties in the two directions or on adjustment ofthe modulus.

Material obtained by mixing the three polymers A, B and C needs noplasticizers, which cause migration problems, especially in the case offood packaging. However, quantities of plasticizer of less than 5% ofthe polymers (B+C) can be added.

Various other additives can be incorporated into the mixture, such asanti-oxidants, UV stabilizers, heat and hydrolytic stabilizers, flameretardants, slow-release agents or organic or inorganic fillers such asnatural fibres, anti-static agents, humectant agents, colourings orlubricants, for example.

In particular, in the production of film by the blown or cast methods,silica, calcium carbonate, talc, kaolin, kaolinite, zinc oxide andvarious wollastonites can be added, as can, generally speaking,inorganic lamellar substances functionalized or not with organicmolecules, which are able to delamellate during the mixing stage withthe polymeric mixture, or with one of the individual polymers thereof,so as to form nanocompounds with improved anti-blocking and barrierproperties. The various inorganic substances can be used in combinationor individually. The concentration of inorganic additives is generallyof between 0.05 and 70%, preferably of between 0.5 and 50% and, evenmore preferably, of between 1 and 30%. Particularly preferred arewollastonites and similar organophile substances.

In the case of natural fibres and fillers, such as cellulose, sisal,ground nuts, corn husks, rice husks, soya and the like, preferredconcentrations are of between 0.5 to 70%, preferably of between 1 and50%. It is also possible to bulk out these materials with mixedinorganic and plant matter.

Aliphatic acid amides can be added to improve the film-formingcharacteristics of the material, such as oleamide, stearamide,erucamide, behenamide, N-oleylpalmitamide, N-stearylerucamide and otheramides, salts of fatty acids such as aluminium, zinc or calcium stearateand the like. The quantity of these additives varies between 0.05 and 7parts, and preferably between 0.1 and 5 parts of the polymeric mixture.

The mixture thus obtained can be turned into film by blowing or byextrusion with a flat head. The transparent film is strong, can bebonded perfectly and can be produced in thicknesses of up to 5 μm,either blown or cast. The film can be made into sacks and bags forcarrying goods, film and bags for food packaging, stretchable,heat-shrinkable film, film for adhesive tape, for disposable nappy tapesand for. decorative coloured tape. Some other main applications are forsilage, for “breathable” bags for fruit and vegetables, bags for breadand other food products, film for covering packs of meats, cheese andother food items and yoghurt pots. The film can also be bi-orientated.

Film produced with compounds of the invention can also be used as asealable component in composite materials with at least one layer ofpolylactic acid or another polyester, of starch which has or has notbeen destructured and blends thereof with synthetic or natural polymers,or in a compound material, layered with aluminium and other materials,or can be metallized under vacuum with aluminium, silica or otherinorganic materials. The layers can be produced either by co-extrusionor by laminating or by extrusion coating, provided that one layer ispaper, fabric or non-woven fabric and the other is a biodegradablematerial or another material which will not melt at the temperaturesrequired to extrude the film.

The film can be used for agricultural mulching, possibly with theaddition of UV stabilizers, either in the form of single layer film orco-extruded with a lower-modulus film, as in the case of starch-basedmaterials, in order to improve UV resistance and barrier properties, andto slow down the speed of decomposition in the air and in the soil.

The material thus obtained can also be used to manufacture fibre fortextiles and non-woven fabric, or for fishing nets.

In addition, the non-woven fabric can be used for disposable diapers,sanitary protection and the like. The fibres can also be bonded tospecial types of paper as reinforcement.

The material can also be used successfully to manufacture sheets foreither mono-extruded or co-extruded heat forming, with other polymericlayers such as polylactic acid, other polyesters or polyamides,starch-based materials or other materials, and then heat formed intotrays for food packaging, agricultural containers and the like.

Other additives can also be added to the material, such as polyethyleneor polypropylene waxes, PET and PTB, polystyrene, ethylene or propyleneco-polymers with functional carboxyl groups, carboxylate, methacrylate,acrylate, or hydroxy groups, or it can be combined with such polymers inco-extrusion, co-injection or similar operations. The material can beused as a matrix in a blend with destructured starch, according tomethods related in Patents EP-0 327505, EP-0 539541, EP-0 400532, EP-0413798, EP-0 965615, in which it can bond with the starch.

It can be used as a coating film for biodegradable foam materials basedon polyester, polyamides made from thermoplastic starch, complex starchor simply a blend of starch with other polymers, or with the material ofthe present invention.

The material can also be expanded, alone or mixed with starch or withother polymers for the manufacture of containers for fruit andvegetables, meat, cheese and other food products, of fast foodcontainers or even of foam balls which can be moulded into foam elementsfor industrial packaging. It can be used as a foam in the place ofpolyethylene foam. It can be used in the injection molding field forexample in order to produce cutlery, food containers, containers foragriculture and industry, pharmaceutical containers and so on.

It can also find application in the field of textiles and non-wovenfabric for clothing, hygiene and industrial products, and also forfishing nets or nets for fruit and vegetables.

The mixture of biodegradable polyesters of the invention will now bedescribed by means of some non-limitative examples.

EXAMPLES Example 1

Polymers constituting the mixture:

-   -   50% aliphatic-aromatic polyester (A): Ecoflex 0700 BASF;    -   40% aliphatic polyester (B): Polybutylensebacate made of sebacic        acid and butandiol with a monobutylstanoic acid catalyst, as in        example 1 of WO 00/55236;    -   10% polylactic acid polymer (C): 4040 Cargill with a 6% D-lactic        content (MFI=4 dg/min).

The polymers were mixed in an OMC extruder:

-   -   Diameter 58 mm; L/D=36; rpm=160; heat profile 60-120-160×5−155×2    -   Absorption=80A. Delivery=40 kg/h    -   Film forming on Ghioldi machine:    -   Diameter=40 mm, L/D=30; rpm=45; die: diameter=100 mm; air        gap=0.9 mm; land=12; Delivery 13.5 kg/h    -   Heat profile: 110-130-145×2; filter temperature 190×2; head        temperature=190×2

Film: width=400 mm; thickness 25 μm;

The film thus obtained was subjected to the Elmendorf tear-resistancetest, carried out on a Lorentzen & Wettre pendulum. The test was carriedout both transversely (Ecross) and longitudinally (Elong). The ratiobetween the two values (Ecross/Elong) shows the level of isotropy of thefilm in the two directions.

Transmittance values were determined both at the source port (Tsource)

And at the entrance port (Tentr), was carried out with an XL-211HAZEGUARD SYSTEM measurer.

The modulus of elasticity (E) values, breakage load (σ) and breakageelongation (ε) were determined in accordance with ASTM D 882-91 with anINSTRON-4502 instrument.

The results of the tests are reported in Table 1

Examples 2–11

While maintaining the conditions of mixture extrusion and film formingrelated in example 1, the percentages of the polymers constituting themixture were varied. The results of the tests on the film thus producedare given in Table 1. In Example 10, polybutylensebacate was replacedwith poly-ε-caprolactone. In example 11 polybutylensebacate was replacedwith polybutylensuccinate (Bionolle 1903, Showa Denko).

The results thus obtained demonstrated how the ranges of concentrationof the polymers in the mixture are crucial to the simultaneousachievement of considerable mechanical and transparency characteristicsof the film, which prove so useful in countless practical applications.

Examples for Comparison

While maintaining the conditions of mixture extrusion and of filmforming related in Example 1, binary mixtures were tested, which eachtime contained only two of the polymers constituting the mixture of theinvention. The results of the tests on film thus produced are given inTable 2. In Example 3c, polybutylensebacate was replaced withpoly-ε-caprolactone.

Comparison of the data displayed in the two tables is clear evidence ofthe considerable improvement in the mechanical properties of filmmanufactured with polymeric mixtures of the invention.

TABLE 1 A B C A/ C/ E_(cross) E_(long) E_(cross)/ T_(source) T_(entr) Eσ ε Es % % % A + B A + B + C N/mm N/mm E_(long) % % (Mpa) (MPa) (%) 1 6030 10 66.6 10 47.8 81 0.59 72.7 89 527 36 458 2 50 40 10 55.5 10 44.952.4 0.85 65.2 89.4 549 34 446 3 45 45 10 50.0 10 57.5 20.2 2.84 64.189.6 511 36 490 4 40 50 10 44.4 10 49.3 33.1 1.49 63.5 89.9 576 35 450 550 30 20 62.5 20 32.5 37.4 0.86 61.8 87.0 776 32 354 6 40 40 20 50.0 2037.8 42.9 0.88 45.5 87.8 757 31 353 7 20 40 40 33.3 40 7.4 9.1 0.81 41.288.5 1321 37 319 8 50 45 5 52.6 5 80.2 17.8 4.5 — — 328 32 609 9 50 48 251.0 2 134 12 11.16 — — 242 31 674 10 50 40 10 55.5 10 13.9 10.7 1.3075.0 89.0 567 30 576 11 50 40 10 55.5 10 14.2 13.5 1.02 60.1 88.1 502 37589

TABLE 2 A B C E_(cross) E_(long) E_(cross)/ T_(source) T_(entr) E σ εEs. % % % N/mm N/mm _(long) % % (Mpa) (MPa) (%) 1a 0 50 50 7.1 6.4 1.168.5 93 2007 35 60 1b 0 60 40 10.7 5.1 2.09 38.5 90.4 1464 36.5 362 1c 040 60 7.8 8.6 0.90 73 92 2018 34 69 2a 50 0 50 8.1 7.2 1.1 57.3 85.61416 39 394 2b 60 0 40 12.8 7.8 1.64 36.5 82.1 1122 39 361 3a 60 40 0194 6.98 27.8 65 87 215 42 499 3b 50 50 0 219 6.14 35.7 75 93 245 41 4523c 50 50 0 246 8 30.8 80 90 — — — 3d 30 70 0 84.8 7 12.1 — — 281 42 426

1. A mixture of biodegradable polyesters which includes: (A) an aromatic-aliphatic polyester wit a melting point of between 50° and 170° C.; (B) an aliphatic polyester with a molecular weight M_(w) greater than 40,000 and a melting point of between 40° and 170° C. ; (C) a polylactic acid polymer which contains at least 75% of L-lactic or D-lactic acid, or combinations thereof, with a molecular weight M_(w) greater than 30,000, in which the concentration of A varies with respect to (A+B) in the range of between 40 and 70% by weight and the concentration of C with respect to (A+B+C) is of between 5 and 30%.
 2. A mixture of biodegradable polyesters according to claim 1, in which the modulus of the aromatic-aliphatic polyester (A) is less than 150 MPa and its elongation to breaking is greater than 500% for film with a thickness of between 25–30 μm produced by the blown method.
 3. A mixture of biodegradable polyesters according to claim 1, in which the modulus of elasticity of the aliphatic polyester (B) is of between 200 and 1500 MPa and its elongation to breaking is greater than 25% for film with a thickness of between 25–30 μm, produced by the blown method.
 4. A mixture of biodegradable polyesters according to claim 1, in which the modulus of the polylactic acid polymer (C) is greater than 1,500 MPa.
 5. A mixture of biodegradable polyesters according to claim 1, in which: the aromatic-aliphatic polyester (A) has a modulus of less than 150 MPa, elongation to breaking of more than 500% for film with a thickness of 25–30 μm, produced by the blown method; the aliphatie polyester polyester (B) has a modulus of elasticity of between 200 and 1500 MPa, elongation to breaking of more than 25% for film with a thickness of 25–30 m, produced by bubble forming; the polylactic acid polymer (C) has a modulus greater than 1,500 MPa.
 6. A mixture of biodegradable polyesters according to claim 1 in which the aromatic-aliphatic polyester is biodegradable according to standard CEN
 13432. 7. A mixture of biodegradable polyesters according to claim 1 in which the melting point of the aromatic-aliphatic polyester (A) is of between 50° and 170° C.
 8. A mixture of biodegradable polyesters according to claim 1 in which the molecular weight of the aliphatic polyester (B) is M_(w)>40,000, and its melting point is of between 40° and 170° C.
 9. Mixture of biodegradable polyesters according to claim 1 in which the polyester (B) is of the diacid/diol type.
 10. Mixture of biodegradable polyesters according to claim 1 wherein the polyester (B) is a polyhydroxyacid.
 11. Mixture of biodegradable polyesters according to claim 10 wherein the polyester (B) is polycapralacton and/or its copolymers.
 12. Mixture of biodegradable polyesters according to claim 10 wherein the polyester (B) is a polyhydroxyalcanoate.
 13. Mixture of biodegradable polyesters according to claim 9 wherein the aliphatic polyester (B) contains as diacid, azelaic acid, sebacic acid, brassilic acid, or mixtures thereof in a concentration, with respect to the total acid content, higher than 50 % moles.
 14. Mixtures of biodegradable polyesters according to claim 1 together with destructurized starch, native starch or modified starch wherein the starch, either complexed or not complexed, is present in a dispersed phase.
 15. Film produced from mixtures of biodegradable polyesters according to claim
 1. 16. Film according to claim 15, characterized by tear resistance in both directions, according to the Elmendorf test, of between 10 and 100 N/mm.
 17. A film according to claim 16, characterized in that the ratio of transverse to longitudinal tear resistance, according to the Elmendorf test, is between 4.5 and 0.4.
 18. Film according to claim 15 characterized in that the modulus value is of between 150 and 1200 MPa.
 19. Food packaging, or packaging for containing organic residue or for agricultural mulching comprising the film according to claim
 15. 20. Compact sheet manufactured with mixtures according to claim 1 for food containers, containers for seedlings and industrial containers in general.
 21. Foam sheet manufactured with mixtures according to claim 1 for food or other containers or for industrial packaging.
 22. Fibres manufactured with mixtures according to claim 1 for textiles and non-woven fabrics used in the hygiene, fashion and industrial sectors.
 23. A coating material manufactured with mixtures according to claim 1 for application to paper, textiles, non-woven fabrics or other layers of compact or expanded biodegradable material.
 24. A mixture of biodegradable polyesters according to claim 1 wherein the concentration of C with respect to (A+B+C) is between 5 and 20% by weight.
 25. A mixture of biodegradable polyesters according to claim 1 wherein the elongation to breaking of the aliphatic polyester (B) is >100%.
 26. A mixture of biodegradable polyesters according to claim 5 wherein the elongation to breaking of the aliphatic polyester (B) is >100%.
 27. A mixture of biodegradable polyesters according to claim 1 in which the melting point of the aromatic-aliphatic polyester (A) is of between 80° and 120° C.
 28. A mixture of biodegradable polyesters according to claim 1 in which the molecular weight of the aliphatic polyester (B) is >60,000, and its melting point is of between 50° and 145° C.
 29. A mixture of biodegradable polyesters according to claim 1 in which the molecular weight of the aliphatic polyester (B) is >60,000, and its melting point is of between 55° and 130° C.
 30. Mixture of biodegradable polyesters according to claim 9 wherein the aliphatic polyester (B) contains as diacid, azelaic acid, sebacic acid, brassilic acid, or mixtures thereof in a concentration, with respect to the total acid content, higher than 70% moles.
 31. Film according to claim 15, characterized by tear resistance in both directions, according to the Elmendorf test, of between 15 and 90 N/mm.
 32. Film according to claim 15, characterized by tear resistance in both directions, according to the Elmendorf test, of between 20 and 80 N/mm.
 33. Film according to claim 15 characterized in that the modulus value is of between 250 and 1000 MPa.
 34. Mixture of biodegradable polyesters according to claim 1 in which the polyester (B) is of the diacid/diol type selected from the group consisting of polybutylensebacate, polybutylenazelate, polyethylensebacate, polyethylenazelate, polybutylensuccinate, polybutylenbrassilate, polybutylenazelateadipate, polyallcylenbrassilate. 